Write heads are used in combination with a magnetic medium to record data thereto. The magnetic medium, which may be in the form of a magnetic disc, includes a storage layer. The write or recording head is configured to generate a magnetic field that aligns magnetic moments of the storage layer to represent the desired bits of data.
Magnetic recording techniques include both longitudinal and perpendicular recording techniques. Perpendicular recording is a form of magnetic recording in which magnetic moments representing bits of data are oriented perpendicularly to the surface of the storage layer of the recording medium, as opposed to longitudinally along a track of the medium as in the more traditional longitudinal recording technique.
Perpendicular recording techniques have the potential to support higher linear areal recording densities than conventional longitudinal designs. One factor that plays a role in the areal density at which a perpendicular write head is capable of recording data to the magnetic medium is the head-media spacing (HMS). The HMS is the distance between the write head and the magnetic medium. Performance of the write head is very sensitive to the HMS. In particular, as the HMS is reduced, the areal recording density capability of the write head increases. However, the HMS must also be large enough to avoid contact between the write head (or the slider supporting the write head) and the magnetic medium.
Perpendicular magnetic write heads typically include main and return poles that are separated by a write gap. The main and return poles each extend from pole tips located at an air-bearing surface (ABS) to a back gap region. A back gap portion typically connects the main and return poles together at the back gap region to form a magnetically conductive path therebetween. A coil typically surrounds the back gap portion and is used to generate magnetic signals through the main and return poles in response to a current conducted therethrough. The magnetic signals are focused at the main pole tip such that they interact with a storage layer of a magnetic medium to orient a vector of magnetization in an up or down direction. The orientation of the magnetization in the storage layer of the magnetic medium represent bits of data. The return pole conventionally has a very large volume relative to the main pole. Additionally, the return pole has a large cross-sectional area taken parallel to the ABS in order to prevent the generation of an erasure field that could inadvertently reorient the magnetization in the storage layer of the magnetic medium. Unfortunately, the large return pole can limit the performance of the write head by limiting the minimum HMS for the write head due to thermal induced protrusion of the return pole.
The write head is generally comprised of a substrate and several metallic and insulating layers. During operation, the head is subjected to increased temperatures due to head dissipation in the head caused by the generation of magnetic recording signals by the passing of a current through a coil of the head. As the temperature of the head increases, the metallic layers expand more than the insulating layers. As a result, the metallic layers tend to protrude closer to the magnetic medium than the insulating layers, which affects the HMS and, thus, the recording capability of the write head.
The change in HMS caused by such an expansion is typically referred to as a thermal pole tip protrusion (TPTP). TPTP has become increasingly significant due to a need to reduce the HMS in order to meet the increasing demands for higher areal density recording capabilities. The return pole is most sensitive to such protrusion due to its large size relative to the main pole. Thermal induced protrusion of the return pole affect the performance of the write head in primarily two ways. First, the protrusion of the return pole at elevated temperatures increases the possibility of head-disc contact, which sets a limitation of the HMS. Second, the return pole can contribute to reduced write head performance, such as a reduction of writeability, write field gradient, and signal-to-noise ratio, as a result of an increase in the HMS due to a recession of the return pole at low temperatures.
Accordingly, a need exists for a return pole of a perpendicular write head having low thermal induced protrusion while reducing the generation of erasure fields.